Chlamydia trachomatis is one of the most common causes of blindness and sexually transmitted diseases in humans. C. trachomatis is an obligate intracellular bacterium which is biphasic. The intracellular form is the metabolically active reticulate body and the extracellular form is the infectious elementary body (EB) (Moulder et al. (1984) in Bergey's Manual of Systemic Bacteriology (Krieg, ed.) 1:729–735, Williams & Wilkins, Baltimore).
A prominently exposed component on the surface of the chlamydial EB involved in the initial interaction between C. trachomatis and the host cell is the major outer membrane protein (MOMP; Mr 40,000) (Caldwell & Judd (1982) Infect. Immun. 38:960–968). The MOMP is the principal structural protein of the EB and individual MOMP proteins are cross-linked by disulfide bonds to provide rigidity to the cell wall (Newhall & Jones (1983) J. Bacteriol. 154:998–1001). The serologic specificity of the organism resides in the MOMP and antibodies raised to MOMP can neutralize infectivity of chlamydia (Caldwell & Perry (1982) Infect. Immun. 38:745–754; Lucero & Kuo (1985) Infect. Immun. 50:595–597).
MOMP and two other chlamydial proteins (Mr 32,000 and 18,000) were identified as glycoproteins when the organisms were probed with various plant lectins (Swanson & Kuo (1990) Infect. Immun. 58:502–507). Further characterization showed the three proteins to be glycosylated by way of N-linkage, a structure means rarely found in bacteria (Wieland (1988) Biochimie, 70:1493–1504).